Conventional lamp devices, such as Post Cap Lamp and Decorative Lamp Post disclosed in U.S. Pat. Nos. 3,866,034 and 5,178,454 respectively, inevitably have some drawbacks that, for example, a lamp socket and bulb have to be set only on lamp cover decoration or a bulb can not be positioned in the location as required. In general, it is the best way that the bulb can be fixed at the center of the decoration. It is an object of the invention to provide a lamp device, in which a lamp socket and cover can be fixed on post to achieve convenience and stability for use, thereby solving the problem in prior art.